Shoulder mechanisms are known that include a first element that is secured to the user of the mechanism. The first element may be stationary, or worn by the user. A second element is hinged to the first element about a first hinge axis that is substantially horizontal, extending in a longitudinal direction that extends from front to back relative to the user. A third element is hinged to the second element about a second hinge axis that is substantially vertical when the mechanism is at rest (i.e. when the user's arm extends down along the user's body), the second hinge axis being perpendicular to the first hinge axis. Finally, the upper arm proper of the mechanism is hinged to the third element about a third hinge axis that is once more substantially horizontal, and that is substantially perpendicular to the first and second hinge axes.
Shoulder mechanisms are known in which the three hinges are made by means of successive pivots. Nevertheless, such mechanisms generally present interference with the user's arm while the arm is being moved. In particular, the second pivot, i.e. the pivot constituting the hinge of the third element on the second element, is carried by the second element so as to extend above the shoulder, such that when performing an abduction movement of the arm, the second pivot comes very quickly into the vicinity of the user's head, thereby greatly limiting the permissible amplitude of the abduction movement.
Proposals have been made to provide the hinge between the third element and the second element by means of a slideway that extends along a circular arc, the arc extending horizontally at rest so as to go around the user's shoulder. Such an arrangement presents numerous advantages, in particular the advantage of minimizing interference between the mechanism and the user during ordinary movements of the arm.
Nevertheless, such an arrangement can present certain drawbacks. An abduction movement of the user through angles close to 90 degrees brings the slideway into the vicinity of the user's face, and that can be troublesome. Furthermore, for practical reasons of implementation, it is difficult for the radius of the slideway to be made smaller than 100 millimeters, which prevents making orthosis mechanisms that are suitable for children. Furthermore, the slideway is subjected to large amounts of bending, which can lead to mechanical weakness, and also to an increase in friction.